Written by Aimee Bradshaw Reviewed by James Macey Updated on 20 April 2023 On this page What is SIP trunking? SIP trunk providers in the UK 8×8 FlowRoute Net2Phone Free SIP providers in the UK How We Ranked the Best SIP Providers Expand Our site is reader-supported – by clicking our links, we can match you with a potential supplier, and we may earn a small commission for this referral. According to our research, the best SIP trunking providers are 8×8, FlowRoute, and Net2Phone.As VoIP (voice over internet protocol) phone systems become the norm, businesses have had to learn a new set of terminology. Session Initiation Protocol (SIP) is a standardised set of communication formats used in VoIP, instrumental in the sending of voice and video messages over a VoIP phone system. In recent years, SIP trunking has replaced standard phone system trunking, bringing a higher level of efficiency and quality to calls. Save by comparing telephone systems quotes from leading suppliers Do you already have a business telephone system? Yes No Just answer a few questions – it only takes a minute What is SIP trunking?Many business phone systems are hosted on a Private Branch Exchange (PBX), which eliminates the need for an individual line to be run to each desk in an office. To communicate with the outside world, businesses use trunking, which is in essence a pipe leading calls from the office to the public switched telephone network (PSTN).The PSTN network will be switched off by December 2025, which means phone lines will need to be switched over to a digital network.SIP trunking allows a business to make full use of an IP-based PBX, replacing traditional PSTNs with a PSTN from an internet-based SIP trunk provider. In the process, an SIP trunk can reduce a business’s overall costs and improve reliability for video conferences. For this reason, many businesses are making the switch.Learn more about the differences between SIP and VoIP on our page. SIP trunk providers in the UKBusinesses today can choose from a wide variety of SIP trunk providers, many of which offer affordable, high-quality services. 8×8 8x8 Pricing Bespoke Get free quotes 8x8 Review Quick overview 8×8 offers free point-to-point calling between a business and other 8×8-enabled sites, as well as unlimited concurrent calls. 8×8 also offers virtual numbers, which means local numbers can be set up in a variety of cities to make it easier for customers to call for assistance. The company’s SIP pricing is based on a business’s unique needs, with prices changing as a business grows and more numbers and features are added. Read more + Read less - FlowRoute FlowRoute Get free quotes Quick overview Developed by telecom-savvy developers, FlowRoute is designed to provide simplified, scalable, and direct access to a global network of VoIP users. FlowRoute offers phone numbers for £0.90 per month with outbound rates at £0.0070 per minute. The system uses detailed routing intelligence to manage calls for more advanced phone system functionality. Read more + Read less - Net2Phone net2Phone Get free quotes Quick overview Net2Phone is an internet-based calling service that works with any PBX phone, making it ideal for businesses that already have PBX equipment in place. The service offers unlimited concurrent calls, no monthly contracts, and high-quality, low-cost calling. Customers pay as they use the service, with simplified, per-minute pricing that might be more suitable to businesses with low call volumes. Read more + Read less - Free SIP Providers in the UKThere are several providers that offer free SIP trunking, but these services can be of poorer quality than paid services. However, if your budget is very tight you could consider one of the following options:OnSIP provides mobile and desktop voice and videoconferencing.SIP2SIP offers audio, video, presence, chat, file transfer, and conferencing.Antisip offers toolkits for mobile and desktop platforms.With so many excellent providers, businesses can shop around to find the best pricing and features to meet their needs.For organisations with existing PBX equipment, an option that works with the hardware already in place can save a great deal on initial set-up costs. How We Ranked the Best SIP ProvidersAt Expert Market, we spend time researching, testing, and evaluating providers we write reviews about. This typically consists of conducting market research to narrow down the software that's really worth digging into a little more and then assessing it against a range of research criteria.Our Decision-Making Criteria with Assessment WeightingInformed by readers and businesses we speak to regularly, as well as our own experiences using major VoIP platforms, we designed a research framework to assess each VoIP provider plan. It consists of eight overarching assessment categories, each designed to answer a specific question a buyer might have.Which VoIP service offers the best call handling features for UK businessness?Call management (25%) – We assessed features like call routing, queues, custom greetings, voicemail screening, and spam call blocking to see how well each provider handles inbound traffic.Can this platform support internal communication across remote or hybrid teams?Communication channels (20%) – We looked at the availability of tools like video conferencing, team messaging, SMS, and mobile app functionality.Will this system help me onboard and train staff effectively?Training features (20%) – We tested tools for live coaching (e.g. call whisper/barge), call recording, and performance dashboards — crucial for service and sales teams.Is the pricing clear and competitive for small and medium businesses?Pricing (10%) – We reviewed subscription tiers, user discounts, setup fees, and whether unlimited minutes are included or capped.Will this VoIP system work with the software we already use?Software integrations (10%) – We checked how well each provider integrates with platforms like Salesforce, HubSpot, Zendesk, Google Workspace, and Microsoft Teams.Can we keep using our existing phones and hardware?Hardware integrations (5%) – We reviewed compatibility with desk phones, speaker systems, and headsets from major brands.What level of customer support is available if we run into issues?Customer support (5%) – We tested the availability of live chat, phone, and email support, as well as help centres and user communities.How secure is this system for business use?Security options (5%) – We assessed features like multi-factor authentication (MFA), encryption, and compliance with UK data protection laws (e.g. GDPR). Written by: Aimee Bradshaw Writer and researcher Aimee is Expert Market’s resident telephone systems and point of sale go-to. If she’s not writing about business products, you’ll find her daydreaming about dog walking on Dorset beaches. Reviewed by: James Macey Senior Business Software Researcher James draws on his 4+ years experience as a researcher to offer specialized advice on a wide range of categories from CRM to Fleet Management. He believes all businesses can grow if they use the right tools and services.